1. Field of the Invention
This invention is directed generally to the field of Radio Frequency (RF) identification systems employing an electronic transponder and a transponder reader which emits an RF interrogation signal at a first frequency which powers the electronic transponder and enables it to transmit a response on a second frequency (usually a lower frequency). Such systems are used in a number of fields including access security, object identification, inventory control, and generally any field where a small transponder unit may be associated with an object and remotely probed and read by a radio frequency transmission emitted by a transponder reader.
2. The Background Art
Radio frequency identification systems are well known in the art. Such systems are commonly in use in building access schemes where an authorized user of the building is given a building access card containing an authorization code number stored and optionally encrypted on the card as a binary string of data. The card is then presented to a transponder reader which continuously transmits an RF interrogation signal. The card containing a transponder receives the continuously transmitted signal from the transponder reader, uses it to power circuitry on board the card, modulate an RF carrier signal having a different frequency (usually lower) from that of the RF interrogation signal received from the reader (typically an integer fraction of the RF interrogation signal frequency, e.g., {fraction (1/2, 1/3, 1/4)}, etc.) with an identification signal stored on the transponder and containing an authorization code number, and the transponder reader then reads the identification signal emitted from the transponder and passes the authorization code number to an appropriate controller for determining whether or not the authorization code number received is sufficient to allow the user access to the building. If the authorization code number is sufficient, generally a lock will be opened enabling a door to be opened and optionally a computer will log the entry for future reference.
Other implementations of such systems enable object identification by reading a transponder attached to or embedded in the object (e.g., cargo identification, pet identification, taxi identification at an airport, and the like).
Generally, all existing transponder readers of such radio frequency identification systems utilize proprietary systems. That is, a card from one system will not be readable by a system provided by another vendor. In some systems, the transponder emits a signal modulated by frequency shift keying (FSK), i.e., the binary transmission is represented by a mark and a space which correspond to the 1 and 0 of the binary signal, the mark and space being signals on two separate frequencies (e.g., xe2x85x9 and {fraction (1/10)} of the frequency of the RF interrogation signal). Other systems utilize phase shift keying (PSK) as well known in the art. Systems using PSK modulation cannot read the cards which transmit FSK modulated information and systems which read FSK modulated information cannot read the cards which transmit PSK modulated information.
While all such transponder readers read matching transponder cards, in most systems they are also required to communicate with a controller of some sort. The controller generally comprises a central processing unit (CPU) which may interact with a number of such readers which are simultaneously connected to it. A number of different systems have evolved over the years for communicating data from a reader to a controller. Some of these systems, or communications protocols, are known as magnetic stripe communications protocol, Wiegand communications protocol, single wire Wiegand communications protocol, RS232 communications protocol, RS422 communications protocol, and the like. These various communication protocols generally require 1, 2, 3 or more electrical wire connections between the transponder reader and the controller. Furthermore, the data modulation schemes for these various systems differ as well known to those of ordinary skill in the art. This has led to a problem in the industry in the stocking of transponder readers. In order to stock transponder readers which are compatible with the various communications protocols employed by the various controllers, one needs to stock many transponder readers which are mutually incompatible with one another. A need, therefore, exists for a transponder reader which is capable of working with a number of different communication protocols in communicating with a corresponding controller so as to reduce the inventory requirements for transponder readers.
It is also desirable to have the transponder reader require as little field programming as possible. In this way, relatively unskilled personnel may successfully install transponder readers and have them operate with corresponding controllers and transponders with relatively little difficulty. To avoid the necessity to physically program such readers to communicate using a given communications protocol (as by setting DIP switches or jumpers) would be highly desirable.
Accordingly, it is an object and advantage of the present invention to provide an improved RF identification system.
It is a further object and advantage of the present invention to provide an improved transponder reader for use in RF identification systems.
It is a further an object and advantage of the present invention to provide a capability to program the transponder reader to communicate with an attached controller using a communications protocol specified by information contained in an output format identification portion of the identification signal stored in the transponder and transmitted to the transponder reader.
It is a further object and advantage of the present invention to provide an improved transponder for use in an RF identification system.
It is a further object and advantage of the present invention to provide a transponder for use in an RF identification system which contains an identification signal which has within it, in addition to an authorization code number, an output format identification portion which, when transmitted to and received by the transponder reader, defines the communications protocol to be used by the transponder reader in communicating with attached devices such as a controller.
Yet another object and advantage of the present invention is the provision of a transponder reader capable of reading both PSK and FSK signals.
Yet another object and advantage of the present invention is the provision of a mechanism by which either the PSK or the FSK mode of operation may be normally disabled and easily authorized in an accountable manner.
These and many other objects and advantages of the present invention will become apparent to those of ordinary skill in the art from a consideration of the drawings and ensuing description of the invention.
A radio frequency identification system includes a transponder and a transponder reader. The transponder, responsive to an interrogation signal continuously transmitted by the transponder reader, generates a transponder signal modulated by an identification signal readable by the transponder reader. The identification signal includes a synchronization portion, a data portion, an output format identification portion, and an error detection portion. The output format identification portion is used by the reader to configure itself for communication with an attached controller. In another aspect of the invention, the transponder reader may be configured to read FSK as well as PSK encoded signals from the transponder.